The present invention relates to alpha-methylstyrene dimers and derivatives thereof and to processes of making the same.
Alpha-methylstyrene dimers (AMSDs) may be used as addition fragmentation chain transfer agents in processes of making polymers by free radical polymerization. During polymerization reactions, chain transfer agents may be added to propagating radicals and undergo fragmentation to create new radical forms. AMSDs, unlike some other chain transfer agents, are odorless, easy to handle, and do not cause discoloration or influence the stability of polymers. Additionally, they provide a method of molecular weight control, and AMSD containing functional groups such as hydroxyl, vinyl and amino groups enhance reaction with other functional groups so that polymers formed thereby may be considered telechelic. Telechelic polymers are macromolecules having chains of polymerized monomer comprising reactive functional groups at the terminal ends of the chains. Telechelic polymers are widely used in the synthesis of specialty polymers.
One method of making AMSDs is by the cationic method as described by Savamoto et. al., Macromolecules 14, 467(1981). Though this method provides a fairly inexpensive method of making AMSDs, the method is unable to produced AMSD derivatives (i.e., AMSDs comprising at least one functional group on one or both rings). Alpha methylstyrene monomers including functional groups may be used as starting materials in cationic methods, but functional groups, such as isocyanato and amino groups, are deactivated by the acid used during these methods. In addition, a cationic process tends to provide low yields of AMSDs of which a substantial percentage exits as an xe2x80x9cinternalxe2x80x9d isomer. Please see FIG. 1. Some commercially available preparations of AMSDs believed to be prepared by a cationic method contain about 7% by weight of AMSDs existing as an xe2x80x9cinternalxe2x80x9d isomer. AMSDs existing as an xe2x80x9cexternalxe2x80x9d isomer (Please see FIG. 2) show significantly higher reaction rates when used in processes of addition chain transfer compared to xe2x80x9cinternalxe2x80x9d isomers which are relatively inert in such processes.
Another method of making AMSDs is by the radical polymerization process. This process is described in Yamada, et al., Journal of Polymer Science, Part A, Polymer Chemistry, Vol. 32, 2745-2754 (1994), which discloses a method of producing alpha-methylstyrene dimers using benzylbis(dimethylglyoximato)(pyridine)cobalt(III) and a reaction temperature of 60xc2x0 C. Unfortunately, the method produces low AMSDs yields. Research performed on the polymerization characteristics of alpha-methylstyrene monomers reveals that polymerization occurs until a ceiling temperature, is reached. Then the polymerization of alpha-methylstyrene monomers into polymeric products is inhibited above the ceiling temperature. Martinet et. al., Journal of Applied Polymer Science, Vol. 65, 2297-2313 (1997) reports an alpha-methylstyrene monomer polymerization ceiling temperature of 61xc2x0 C.
The present invention provides a dimerization process for making alpha-methylstyrene dimers in high yields. The process comprises the following steps:
a) adding a cobalt chain transfer catalyst, a free-radical initiator and an alpha-methylstyrene monomer, in an inert atmosphere, to form a mixture;
b) heating the mixture to a temperature in the range of 65xc2x0 C. to 140xc2x0 C.; and
c) forming alpha-methylstyrene dimers.
The dimerization process yields a solution that comprises greater than 20% by weight, and preferably greater than 50% by weight, of AMSDs.
The present invention also provides alpha-methylstyrene derivatives represented by the formula 
wherein R1, R2, R3, R4, R5 and R6 are each independently selected from group consisting of hydrogen, xe2x80x94CH(O), xe2x80x94CN, isocyanato, thioisocyanato, SO3H and salts and esters thereof, NR7R8, a silane, a halogen, xe2x80x94C(O)OR9, xe2x80x94C(O)NR10R11, xe2x80x94CR12(O), xe2x80x94C(O)OC(O)R13, xe2x80x94C(O)NR14COR15, xe2x80x94OC(O)R16, xe2x80x94OR17, substituted and unsubstituted alkyl, substituted and unsubstituted alkenyl, substituted and unsubstituted alkynyl, and substituted and unsubstituted aryl; R7, R8, R9, R10, R11, R12, R13, R14, R15, and R16 are each independently selected from the group consisting of H, alkyl, aryl, substituted alkyl or substituted aryl; R17 is selected from the group consisting of alkyl, aryl, substituted alkyl or substituted aryl; R1, R2, R3, R4, R5 and R6 cannot all simultaneously be hydrogen; and the alkyl and substituted alkyls have a chain consisting of 1 to 12 carbons.
As used herein, with respect to the present invention, the following shall apply:
xe2x80x9calpha-methylstyrene monomerxe2x80x9d refers to alpha-methylstyrene monomer, derivatives thereof, or combinations of alpha-methylstyrene monomer and derivatives thereof, unless otherwise stated.
xe2x80x9cderivativesxe2x80x9d refer to alpha-methylstyrene monomers comprising one or more functional groups such as amino, isocyanato and hydroxyl groups, for example.
xe2x80x9calpha-methylstyrene dimerxe2x80x9d or AMSD refers to a dimer prepared from alpha-methylstyrene monomers defined above.